1. Field of the Invention
The present invention relates to a semiconductor package, and more particularly, to a power module package having improved heat radiating characteristics.
2. Description of the Related Art
In general, a semiconductor package is mounted on a print circuit board after mounting one or a plurality of semiconductor chips on a chip pad within a lead frame and sealing with epoxy molding compound (EMC) to protect the internal part. However, as high-speed, large scale and highly integrated electronic devices have been rapidly developed in recent times, techniques that allow for low cost, miniature, and lightweight manufacturing are also required for power devices which are applied to automobiles, industrial equipments and household electric appliances. Furthermore power devices requires low noise and high reliability. Thus, power module packages in which a plurality of semiconductor chips are mounted on one semiconductor package become increasingly popular.
FIG. 1 is a cross sectional view of a conventional power module package. The power module package shown in FIG. 1 is disclosed in U.S. Pat. No. 5,703,399 for a semiconductor power module filed on May 15, 1996. Referring to FIG. 1, the power module package has a structure in which a plurality of semiconductor chips constituting a power circuit 9 and a control circuit 8 are mounted on a lead frame 3. Reference numerals 1, 2, 4a, 5a, 5b, 6a, 6b, and 7 denote a heat sink, a resin having good heat transfer properties, a power circuit chip element, a control circuit chip element, a resistance element, an aluminum bonding wire, a gold wire, and an insulating EMC, respectively.
According to the conventional art, in order to effectively give off heat which is generated in the power circuit chip element 4a, the highly heat conducting resin 2 is provided beneath the lead frame 3, and the heat sink 1 made of copper is provided under the lead frame 3 so that it may be slightly separated from the lead frame 3. The resin provided on the top of the lead frame is a general insulating EMC 7 other than the resin 2. In addition, there are a plurality of embodiments in which the heat sink 1 and the lead frame 3 are transformed in order to more effectively radiate heat generated in the power circuit chip element 4a. 
However, the conventional art encounters the following problems. First, since an EMC still remains filled between the rear surface of the lead frame 3 and the heat sink 1 made of copper, there is a restriction of emitting heat generated by the power circuit chip element 4a to the outside of the power module package. Second, use of two different resins within one power module package not only complicates a manufacturing process of the power module package but also makes automation of the manufacturing process difficult. Third, use of a heat sink made of copper and the complicated manufacturing process increases the manufacturing cost.
To solve the above problems, it is an objective of the present invention to provide a power module package which can improve heat radiation characteristic, simplify a process, and lower the manufacturing cost.
It is another objective of the present invention to provide a method of manufacturing the power module package.
Accordingly, to achieve the above objectives, the present invention provides a power module package including: a lead frame having a first surface, to which components for a power circuit and a control circuit are attached and on the center of which a down set is provided, and a second surface, to which a heat sink is attached, and edges on which external terminals are provided; a heat sink having one surface attached directly to the second surface of the lead frame projected by the down set, and the other surface exposed to the outside of a power module package, the heat sink being formed of an insulating material having good heat transfer properties; components for the power circuit which are mounted on a portion of the first surface of the lead frame on which the down set is formed; components for the control circuit which are mounted on the first surface of the lead frame; and an epoxy molding compound which encapsulates the lead frame and the heat sink excluding the external terminals of the lead frame and the one side of the heat sink.
Preferably, the heat sink formed of an insulating material having good heat transfer properties is composed of plastic or ceramic including at least one of Al2O3, AlN, SiO2, and BeO.
Preferably, the heat sink is a pre-bent plate for preventing package warpage and it is pre-bent to less than 100 xcexcm.
Preferably, the heat sink is protruded slightly more than the epoxy molding compound. The heat sink is protruded 0.05-0.1 mm greater than the epoxy molding compound.
The present invention provides a method of manufacturing a power module package. According to the method, a lead frame, on the center of which a down set is provided and on the edges of which external terminals are provided, is prepared. A plurality of chips for serving as a power circuit and a control circuit are attached to a first surface of the lead frame and then wire bonding is performed. The lead frame is positioned to a molding equipment for attaching a heat sink formed of an insulating material to a bottom mold die. The lead frame is sealed by an epoxy molding compound in the molding equipment so that the heat sink may be attached to the second surface of the lead frame on which the down set is formed, and that the external terminals and a surface opposing the surface of the heat sink to which the lead frame is attached may be exposed to the outside. In this case, a groove for fixing the heat sink is formed to a depth of 0.05-0.1 mm from the surface of the bottom mold die of the molding equipment.
The present invention also provides a method of manufacturing a power module package. According to the method, a lead frame on the center of which a down set is provided and on the edges of which external terminals are provided is prepared. A plurality of chips for serving as a power circuit and a control circuit are attached to a first surface of the lead frame and wire bonding is performed. The lead frame is positioned to a molding equipment, in which a protrusion portion for attaching a heat sink to a bottom lower die in a subsequent process is formed. The lead frame is sealed by an epoxy molding compound in the molding equipment so that a recessed surface including the second surface of the lead frame, on which the down set is provided, and the external terminals of the lead frame may be exposed. The heat sink is attached to the recessed portion including the second surface of the lead frame exposed to the outside.
The power module package according to the present invention can effectively radiate heat generated during its operation through a heat sink directly attached to the rear surface of a lead frame on which a down set is formed. Thus, reliability of the power module package can be guaranteed.
Furthermore, a sealing process for the power module package can be performed at one time by using resins having the same properties, thus simplifying a process and being advantageous to automation of the process itself.
Lastly, the power module package uses a low cost heat sink instead of metal thus lowering the manufacturing cost.